1. Field of the Invention
The present invention relates to a test circuit for a flat panel display device, and more particularly, to a test circuit capable of separately testing signal lines and pixels on a substrate of a flat panel display device in different groups.
2. Description of the Related Art
There are different types of flat panel devices (FPD) in the current market, such as the liquid crystal display (LCD), the organic light-emitting diode (OLED) and the plasma display panel (PDP). However, for all kinds of the flat panel display devices, testing the signal lines (e.g. the scan lines and the data lines) and the pixels is a mandatory process when manufacturing the display panel so that the normal operation of the manufactured flat panel display device can be ensured.
The full contact test method and the shorting bar test method are the two methods commonly used to test the signal lines and the pixels on the display panel. Although the full contact testing method can test every signal line and every pixel on the display panel, its testing equipment and the probes are excessively expensive, thus the shorting bar test method is generally used.
FIG. 1 schematically shows a circuit for testing the LCD by using the shorting bar test method disclosed in U.S. Pat. No. 5,852,480. Referring to FIG. 1, a plurality of scan lines 11a˜11b and a plurality of data lines 12a˜12b are intersecting to form on a substrate 10 of the LCD, and a pixel structure 13 is disposed on every intersection of the scan line and the data line. Here, a monochrome LCD is exemplified in FIG. 1, where each pixel structure 13 comprises a thin-film transistor TFT, a pixel electrode PE and a storage capacitor Cst. Wherein, the thin-film transistor TFT is coupled to the scan line and the data line.
The shorting bar 14 is coupled to one end of the odd number scan line 11a, the shorting bar 15 is coupled to one end of the even number scan line 11b. When the test signal is input into the shorting bar 14 through a testing pad G/O, a test result is received at the other end of the odd number scan line 11a. When the test signal is input into the shorting bar 15 through another testing pad G/E, a test result is received at the other end of the even number scan line 11b. Similarly, the shorting bars 16 and 17 are respectively coupled to the odd number data line 12a and the even number data line 12b for testing the odd number data lines and the even number data lines. Accordingly, the signal lines 11a˜11b and 12a˜12b and the pixel 13 can be separately tested in different groups by using the shorting bars 14˜17.
After the test is completed, it is common that the electrical connection between the signal lines on the shorting bars 14˜17 and the substrate 10a is cut off by laser, or in some cases, even the portion outside of the substrate 10a is cut off and the substrate 10a is the only one that remains. However, in the invention disclosed in U.S. Pat. No. 6,100,949, a switch device is configured between the shorting bar and the signal line. In such invention, the connection between the shorting bar and the signal line is turned on by the switch device during testing the signal lines or the pixels. On the other hand, once the test is completed, the connection between the shorting bar and the signal line is turned off by the switch device. Accordingly, an additional step of cutting off the connection is not required in the manufacturing process, and the price may be the increase of the size of the LCD.
FIG. 2 schematically shows a circuit for testing the LCD by using the shorting bar test method disclosed in U.S. Pat. No. 6,392,719. Referring to FIG. 2, a color LCD is exemplified in it, where each pixel structure 23 comprises R, G, B three sub-pixels, wherein each sub-pixel comprises a thin-film transistor TFT, a pixel electrode PE and a storage capacitor Cst.
Moreover, the substrate 20 of the LCD is very similar to the substrate 10 in FIG. 1, and the difference is that the data lines of the substrate 10 are separately tested in an odd number group and in an even number group (that is why two shorting bars 16˜17 are required), whereas the data lines of the substrate 20 are separately tested in R, G, B groups (that is why three shorting bars 26˜28 are required). Therefore, the display characteristics of R, B, G sub-pixels on the LCD can be respectively tested.
For an easy explanation, the design of the shorting bar shown in FIG. 1 is generally referred to as a 2G2D design, and the design of the shorting bar shown in FIG. 2 is referred to as a 2G3D design. In addition, other shorting bar designs, such as the shorting bar designs disclosed in U.S. Pat. Nos. 6,246,074 and 6,801,265 are the modifications of the 2G2D or 2G3D designs. Since the demand for an LCD display quality is higher and higher, the conventional shorting bar design cannot provide more diverse test patterns such as the window or color-bar test pattern to determine the existence of crosstalk and flicker, etc., thus the risk of the product defect is higher.